Atherosclerosis and its complications account for substantial morbidity and mortality in industrialized countries. There is increasing evidence that an important pathogenic event in atherogenesis is adhesion of monocytes to the endothelium overlying the early lesion. While native or resting endothelium is non-adhesive, exposure of endothelial cells to inflammatory cytokines, growth factors, or other pathologic agonists induce the expression of specific adhesion molecules on the cell surface. Interactions of monocyte counter-receptors with these endothelial cell adhesion molecules mediates monocyte recruitment into the lesion. The central premise of this proposal is that engagement of endothelial selectin adhesion molecules with their counter-receptors on monocytes can transduce cellular signals and either independently or through co- operation with other adhesion molecules, amplify monocyte functions and thus promote the atherogenic process. We have obtained preliminary data showing that E-selectin interactions with leukocytes induces leukocyte activation as assessed by TNF release and integrin activation. The primary goals of the proposal are to (A) characterize monocyte activation by selectins, in particular those effector functions of relevance to atherosclerosis. We will study cytokine release, procoagulant functions, fibrinolytic functions, cell mobility and reactive oxygen metabolites release in response to selectin receptor engagement. (B) We will also define the cell signalling mechanisms by which selectins activate monocytes. We will study calcium mobilization, protein phosphorylation, phosphatidylinositol metabolism and other well-defined signalling pathways. (C) We will also study co-operative interactions between selectins and other adhesion receptors in monocyte activation. In particular, we will examine co-operative interactions between E-selectin and the beta2 integrins, CD36, and alpha4beta1. For these studies, cells transfected with cDNAs for these receptors either singly or pairs will be used. A detailed understanding of selectins and monocyte signalling and activation should ultimately translate to possible strategies for intervening atherosclerosis.